1) Field of the Invention
The present invention relates in general to devices used to lift and transport semiconductor substrates and more particularly to wafer handling systems.
2) Description of the Prior Art
Semiconductor manufacturers have a need to lift and transport thin, fragile semiconductor wafers over short distances, for instance, from a storage container to processing equipment. Tweezers are often used for this purpose, although tweezers can scratch and damage the fragile wafer surfaces. Sophisticated vacuum wands are also in use; such vacuum wands, must typically be connected to a central source of vacuum and include a form of trigger or valve for selectively coupling the vacuum to the tip of the tool.
Semiconductor wafers are often stored and processed standing upright next to other wafers in a row in a wafer cassette of some type. The wafers are normally facing in one direction so that the device side done wafer faces the backside of the adjacent wafer. Often the spacing between wafers is tight so that many wafers may fit into a small carrier box or into a processing reactor or furnace. The spacing between wafers can be between about 3 to 7 mm and typically can be about 4.76 mm.
Wafers are moved with a vacuum pencil by inserting the vacuum pencil between two wafers and contacting the tip of the vacuum pencil to the backside of a wafer. The vacuum holds the wafer on to the tip and the wafer is lifted out.
Current vacuum pencils create several problems when used to move wafers, especially wafers that are closely stacked together. One problem is that the device sides of wafers are often scratched when the vacuum pencil is inserted between two wafers. Wafers are positioned in wafer boats so that the device side of one wafer faces the back side of the wafer in front of it. To use a vacuum pencil to pick up a wafer, the operator inserts the vacuum pencil tip between two wafers to contact the back side of the selected wafer. However, the operator often touches the vacuum pencil tip to the device side of an adjacent wafer. This often occurs when an operator accidentally inserts the vacuum pencil tip too far down past the edge of the wafer. When the tip is overextended too far past the wafer edge, a small change in the vacuum pencil position will cause the tip to move against the device side.
Carriers are known and used to support and carry semiconductor wafers during handling and processing wafers. U.S. Pat. Nos. 4,037,830 and 5,195,729 describe such carriers. The disadvantage of these carriers is that they are expensive and require additional space in the processing equipment which reduces the capacity of the processing equipment.
There is a need in the industry for a simple and efficient wafer handling apparatus that eliminates or drastically reduces damage to the wafers during handling.